[TheForge] Something I've forgotten or worse yes I just imagine I once knew.

[wmullett at bright.net]

I think that rule of thumb would be invalid.  Besides chimney area and height, the draw of a chimney is also dependent on exhaust temperature and the temperature of the flue.  A flue that is mostly exterior may cool too quickly to maintain a suitable draft.

---- Original message ----
>Date: Sun, 01 Sep 2013 11:44:07 -0500
>From: theforge-bounces at mailman.qth.net (on behalf of CGRAF <adveniam at att.net>)
>Subject: [TheForge] Something I've forgotten or worse yes I just imagine I once knew.  
>To: Blacksmithing List Sponsored by ABANA <theforge at mailman.qth.net>
>
>Somewhere in the dark recesses I seem to remember a rule of thumb for 
>guesstimating CFM of a flue.
>
>It was something like 2X ( cross section X Height)   So a 10ft stack 
>with a 81 inch cross section would yield about 1600cfm .
>
>I believe this was for a gas or oil fire furnace. I am certain a wood or 
>coal fire would have a different yield due to the lift supplied by the 
>heat being greater.
>
>Anybody able to help me out?
>
>Mike Graf
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